Vacuum tube voltmeter circuit



Dec; 30, 1941. E DRQZ HAL 2,267,820

VACUUM TUBE VOLTMETER CIRCUIT Filed May 8, 1940 INVENTORS Paten'ted Dec. 30, 1941 UNITED STATES PATENT OFFlCE man, Elmhurst, N. Y.,

assignors, by mesne assignments, to E. Leitz,lnc;, a corporation of New York Application May 8,1940, Serial No. 333,924

' G Claims. (c1. fill-951 This'invention relates to voltmeters particularly battery operated vacuum tube voltmeters for use in eiectrometrical titrations. The invention provides a novel vacuum tube voltmeter circuit controlgrid has but little .eflect on the electron emission current. The principal effect is that of changing theipartitioning ratio of the current between the oscillator anode and the plate which for the detection and measurements of low direct ,5 results in a decrease in plate current with a sicurrent potentials such as are produced in the course of electrometric titration. The use of the invention is not limited to electrometrictitration" processes but it may used, for other purposes.

For instance it may be used as a P. H. meter or a general electron tube for the measurement of voltages from any source.

The object of the invention is to provide a novel and improved vacuum tube voltmeter circuit employing a single vacuum. tube, capableof l5 rent consum being battery operated and having an unusually low current drain thereby eliminating frequent battery replacement, yet possessing high stability and sensitivity, low tube grid currents, simmultaneous increase in oscillator anode current. If an A. C. signal were to be placed on, the control grid it. would result in plate and oscillator signals'approximately 180 degrees out of phase.

By connecting the tube in a circuit according to our invention an instrument is obtained in which the effective current or voltage amplification of the input voltage will be approximately double that of prior circuits for the same curption without sacrificing other es sential features such as low. grid currents, and simplicity of construction. Consequently for a given sensitivitythis instrument will consume only half the current of previous circuits resultplicity of design, relatively inexpensive to manu- ,ing in long battery life.

facture and easy to operate.

These objects are accomplished by a novel voltmeter circuit according to our invention. The circuit makes use of a pentagrid converter tube Our' novel circuit is illustrated in the accompanying drawing which is a wiring diagram of the circuit. In the drawing the vacuum tube is designated T and is a tube of the type known as of the type known in the art as a IA'IG tube or 1A7G but, may be any other equivalent type other tubes of this type. With such a tube excellent results may be eiipected. Such tubes are used in the field of-radio communication for the 3 purpose/of mixing a generated signal of a giveh frequency with a signal of another frequency ies, are .marked as follows. BI is a biasing batand they are characterized by the fact that the electron emission current flowing through the tube from-the filament to the plate and through the so called oscillator anode iscontrolledby the which contains a filament F, a plate P and five screen'grid in the order numbered. The batter- ,tery. B2 is the filament battery and B3 the plate battery. M is a, voltmeter. C is the titracontrol grid within the tube so that ordinarily the follows. The .one electrode 6 is connected to the effect of imposing an increasingly negative .D. C. potential on the control grid is to decrease the plate current and which also reduces the translational gain of the tube.

control grid I through the switch SI. The other electrode 1 isconnected through variable resist-,,

We have discovered that such-a tube may be 1 9 batteries BI and B2 a wire 8 leads to the filament used for the measurement of small D. C. po-' tentials of the order of milllvolts which are commonly encountered in electro-chemical phenomena in general and more specifically in electrometric titrations andelectr'ode potentials measf urements. However, ordinarily, it these tubes were to ice-used for the measurements 0! small -D; C. voltages one would connect the oscillator mode to the plate or the oscillator anode would F which is connected back to batteries. by a wire 9 through the other switch SI. Resistance RI and switch S2 are "connected by wire l0. Oscillatorgrid l is connected by-wire' H to the negabe disregarded altogether. In' either. case the anode grid '2 by means of wire -l2.- A variable tube would be converted into an equivalent pent ode of lowmutual conductance and amplification factor. However, we have also discovered that when this typeot tube is connected in our resistance is connected between the other side of the meter and the plate. Another resistance R4 is connected by wire 15 to the meter and to battery BS. circuit an increasing negative potential. on the 5 The operation is as follows. When the apparatus is to be used as a titrimeter the cell C is connected as shown. Switch S2 is closed to connect battery B2 with the filament F to heat the filament. Switch SI is now closed on contact a leaving the control grid 4 in a free position. Variable resistance R6 is now adjusted until meter M reads any value of current/between zero and maximum. Some of the electron current passes from the filament F through the various grids to plate P then via-wire l4 and through resistance R6 to the battery. Some electron current also passes from the filament to the oscillator anode 2, thence by wire l through resistance R4 to the battery. If now the IR drop of the first current through resistance RB should be higher than the IR drop of the second current through The reading of the meter will now be proportional the wire l5 through the resistance R4, then some current will flow through the meter M in an amount necessary to again establish equilibrium. Switch SI is now moved to contact c thus connecting the electrodes in the control. grid circuit. Variable resistance RI which changes the grid bias is then adjusted until meter M reads approximately zero and R2 which is merely a fine control for RI is then adjusted until the meter reads exactly zero.

The solution in cell C is now titrated causing the potential across the electrodes 6 and I to change with the addition of the reagent. The difference in potential between the value existing at the beginning of the titration process and the potential existing at the end of any .given addi tion of reagent can be determined from the reading of the meter.

The end-point of the titration is determined by the usual methods, that is it corresponds to the volume of reagent added where the potential of the cell changes most per unit volume of reagent added and in this particular instance to where the meter deflection changes most per unit volume of reagent added. Since the difference of potential in the cell before and after titration is dependent upon the solution in the cell, the electrodes. and the reagent being added, the apparatus has been provided witha sensitivity control R5 which should be adjusted for any particular titration to such a position that after the titration is over the meter M will be reading approximately full scale. This position can only be determined by an actual trial but once found it will insure maximum sensitivity and convenience in carrying out the titration. Ordinarily, as mentioned in the foregoing one would expect that the control grid 4, when made increasingly negative, would result in a decrease of electron emission current and in turn cause a reduction of current in all collecting anodes, in this instance the oscillator anode grid 2 and the plate P. However, with a tube connected as described the control grid 4 has but little effect on the total electron emission current. Instead, it partitions the ratio of current between the plate and the oscillator anode grid 2 which results in a decrease in plate current and a simultaneous increase in oscillator anode current causing the meter to deflect. The deflection is a measure of the change of both circuits. In this manner M gives twice the deflection for a given current passing through the cathode than could be secured by the use of this type of vacuum tube in any other circuit or by the use of any other types of existing tubes.

If it is desired to use the circuit as a voltmeter then the operation is as follows: The unknown potential to bemeasured is connected across the to the unknown potential. The sensitivity of the meter is of course still controlled by R5. The advantage and utility of this circuit is that one may obtain an adequate sensitivity with a very low anode battery drain. This is an important practical advantage and feature of this invention.

In the foregoing description and in the drawing we have disclosed the use of a selected vacuum tube containing five grid elements which have been given conveniently selected names to indicate their characteristics and functions in the circuit. However, it should be understood that the invention is not limited to the use of the particular tube described and shown. Other tubes may be used. It should be noted that while it is advisable and preferable to connect the oscillator grid l to some point of definite potentialwith respect to the filament, such as for instance indicated at H not essential. is left disconnected and permitted to seek its free grid potential the circuit will operate as described. On the other hand a tube may be selected which does not contain an oscillator grid. In that case the circuit will also function as described provided the disposition of theelements within the tube be such as to function in accordance with the principle of the invention. That is to say, the elements must be disposed so asto yield a partitioning of the total anode current between the two collecting elements, the plate and the grid 2, and such partitioning must be a function of the voltage between two other elements of the tube, the control grid and the filament.

We claim:

1. A vacuum tube voltmeter circuit for detecting and measuring low direct current potentials comprising a vacuum tube having a filament and a plate, an oscillator grid, an oscillator anode grid, screen grids and a control grid between said filament and plate; a heater battery connected to said filament, a plate battery, a connection including a variable resistance between said plate and the positive terminal of the plate battery, a connection including a resistance between said anode grid and the positive terminal of the plate battery, a voltmeter connected across the plate and said anode grid, a connection between said screen grids and the plate battery, the negative terminal of the plate battery being connected to the positive terminal of the heater battery, a connection between said oscillator grid and the filament, and means for connecting the terminals of potentials to be measured grid and the filament.

2. A vacuum tube voltmeter circuit for detecta connection, in the drawing, is

ing and measuring low direct current potentials Even, when the oscillator grid I between said control nected to said filament, a plate battery, a connection including a variable resistance between said plate and-the positive terminal of the plate battery, a connection including a resistance between said anode grid and the positive terminal of the plate battery, a voltmeter connected across the plate and said anode grid, a connection including a resistance between said screen grids and the plate battery, the negative terminal of the plate battery being connected to the'po'sitive terminal of the heater battery, a connection be-' tween said oscillator grid and the filament, and means for connecting the terminals of potentials to be measured between said control grid and the filament.

3. A vacuum tube voltmeter circuit for detecting and measuring low direct current potentials comprising a vacuum tube having a filament and a plate, an oscillator grid, an oscillator anode grid, screen grids and a control grid between said filament and plate; a heater battery connected to said filament, a plate battery, a'connection including a variable resistance between said plate and the positive terminal of the plate battery, a

connection including a resistance between said connection between said oscillator grid and the filament, andmeans for connecting the terminals of potentials to be measured between said control grid and'the filament and means for biasing the-control grid.

5 A vacuum tube voltmeter circuit for detecting and measuring low direct current potentials comprising a vacuum tube having a filament and a plate, an oscillator grid, an oscillator anode grid, screen grids and a control grid between said plate battery being connected to the positive terminal of the heater battery, a connection between said oscillator grid and the filament, and

- means for connecting the terminals of potentials anode grid and the positive terminal of the plate" battery, an ammeter with variable series resistance connected across the plate and said anode grid, a connection includinga resistance between said screen grids and the plate battery, the nega tive terminal of the plate battery being connected to the positive terminal .of the heater battery, a connection between said oscillator grid and the filament, and means for connecting the terminals of potentials to be measured between said control grid and the filament. 4. A vacuum tube voltmeter circuit for detecting and-measuring low direct current potentials comprising a vacuum tube having a filament and a plate, an oscillator grid, an oscillator anode grid, screen grids and a control grid between said filament and plate; a heater battery connected to said filament, a plate battery, a connection including a variable resistance between said plate and the positive terminal of the plate battery, a connection including a resistance between said anode grid and the positive terminal of the plate battery, an ammeter with variable series resist-' ance connected across the plate and said anode grid, a connection including a resistance between the plate, battery, the negative terminal of the said screen grids and the plate battery, the negative terminalof the plate battery being connected to the positive terminal of theheater battery, a

to be measured between said control grid and the filament and. means for biasing the control grid. l I

6. A vacuum tube voltmeter for detecting and measuring low direct current potentials comprising a vacuum tube having a plate, an emitting element and a plurality of vacuum tube grid elements therebetweemsaid grid elements including a collecting grid element and a control grid element so disposed as to yield a partitioning of the total anode current between said plate and said collecting grid element, which partitioning is a function of the voltage between said emitting element and said control grid element, a plate battery,'a connection including a variable resistance between said plate and the positive terminal of the plate battery, a connection between said collecting grid element and the positive terminal of plate battery being connected to said emitting element, means for connecting the terminals of potentials to be measured between said control grid element and the said emitting element, and a voltmeter connected across the plate and said collecting grid element to indicate the measurements of potentials.

' MARCEL E. DROZ.

R AYMOND L. GARMAN. 

